1. Field of the Invention
The present invention relates to a separator for various kinds of fuel batteries.
2. Description of the Related Art
An apparatus which uses hydrogen, fossil fuel, or the like, as fuel for directly converting chemical reaction energy generated in an oxidation reaction of the fuel into electric energy is known. This apparatus is generally called a fuel battery.
There are several kinds of fuel batteries. A fuel battery called a solid polymer type is known as one of these kinds of fuel batteries. As shown in FIG. 5, the solid polymer type fuel battery 100 has a structure in which a large number of cells are connected in series or in parallel. Each of the cells has a structure fin which a positive electrode 10, an electrolyte 11 of a sold polymer, a negative electrode 12 and a separator 101 are laminated successively. Further, generally, supporting power collectors 13 are interposed between the electrodes 10 and the separators 101 and between the electrodes 12 and the separators 101.
Each of the separators 101 has channels (grooves) 104 formed in both surfaces. Fuel gas or oxidizer gas is supplied to the respective channels 104 through fuel gas introduction holes 101a and oxidizer gas introduction holes 101b. Further, the separator 101 has cooling water introduction holes 101c to form a structure in which cooling water is made to flow through the holes 101c. 
The operation of a basic fuel battery 100 is as follows. Incidentally, description will be made with attention paid to one cell in order to simplify the description.
In the operation, fuel gas to be oxidized, such as hydrogen, or the like, is supplied to the negative electrode 12 whereas oxidizer gas, such as oxygen, air, or the like, is supplied to the positive electrode 10. The fuel gas and the oxidizer gas are introduced respectively through the fuel gas introduction holes 101a and the oxidizer gas introduction holes 101b of the separator 101 and flow through the channels 104 formed in the opposite surfaces of the separator 101.
In the negative electrode 12, the fuel gas is decomposed into electrons and cations (protons in the case where hydrogen is used as fuel) by the action of a catalytic material.
The cations generated in the negative electrode 12 move to the positive electrode 10 while passing through the electrolyte 11, so that the cations come into contact with the oxidizer gas such as oxygen, or the like, flowing in the positive electrode 10.
The positive electrode 10 is connected to the negative electrode 12 through a load (not shown). The electrons generated in the negative electrode 12 move to the positive electrode 10 through the load.
In the positive electrode 10, the cations of the fuel which have passed through the electrode 11 are oxidized by an oxidizer. When, for example, hydrogen and oxygen are used as fuel gas and oxidizer gas respectively, an oxidation reaction of oxygen and hydrogen occurs in the positive electrode 10.
On this occasion, electrons separated from the fuel in the negative electrode 12 move from the negative electrode 12 to the positive electrode 10 through the load to thereby contribute to the oxidation reaction in the positive electrode 10. Electromotive force is generated by the movement of the electrons.
The fuel battery 100 generally has a structure in which a large number of cells are laminated to be connected in series so that a predetermined voltage is obtained. The number of cells to be laminated is generally from the order of tens to the order of hundreds or more.
Further, in the structure in which such a large number of cells are laminated, adjacent cells are separated from each other by the separator 101.
Except for the edge portion of the laminated structure, the fuel gas such as hydrogen, or the like, flows through one surface of the separator 101 and the oxidizer gas such as oxygen, or the like, flows through the other surface of the separator 101.
Because the fuel gas and the oxidizer gas must not be mixed with each other, it is a matter of course that the separator 101 requires a function of separating the two gases from each other. That is, the separator 101 requires gas-tightness so that no gas permeates through the separator 101 per se.
Further, because the separator 101 serves also as a member for electrically connecting the laminated cells to each other directly, the separator 101 requires a high electrically conductive property (low resistance) as the quality of the material thereof.
Further, the separator 101 requires resistance to water generated as a result of oxidation (water resistance), corrosion resistance to electrolyte contained in the electrolyte 11 and corrosion resistance to the oxidizer.
Further, because a strong compressing force is applied to the separator 101 in a condition that cells are laminated one another, the separator 101 requires great strength to withstand the compressing force.
As configuration for satisfying the aforementioned requirements, there are the following techniques.
One of the techniques is a technique of obtaining the separator 101 by cutting a block which is obtained by baking a vitreous carbon material also called glassy carbon (baked carbon).
Channels 104 are formed in the separator 101 so that the fuel gas and the oxidizer gas are made to flow through the channels 104. Because glassy carbon is deformed greatly when baked, such a method that the separator 101 is produced by baking glassy carbon after molding the glassy carbon in a non-baked state cannot be applied. It is, therefore, necessary to obtain a required shape by cutting a glassy carbon block after the block is obtained by baking.
The baked glassy carbon is, however, so hard that high cost is required for cutting such baked glassy carbon. Furthermore, cutting loss occurs, so that the material is wasted. In view of this point, high cost is also required.
As another technique for obtaining the separator 101, there is a method of obtaining the separator 101 from a mixed or kneaded matter. The mixed or kneaded matter is prepared by mixing or kneading a resin with a carbon type electrically conductive filler such as graphite powder or expansive graphite powder.
In this method, a predetermined shape can be obtained at a low cost by molding or hot-pressing. That is, a predetermined channel structure (a gas path structure which makes gas flow evenly) can be obtained relatively easily.
Although it is preferable, from the standpoint of electric power generating efficiency, that the electrically conductive property of the separator 101 is high, the amount of the electrically conductive filler to be mixed must be increased for obtaining the high electrically conductive property. As a result, there arises a problem that both strength and movability are lowered. Further, because the starting material is powder, there is another problem that dimensional stability in molding is bad.
Further, the separator 101 requires a function of enclosing the fuel gas and the oxidizer gas in predetermined channels 104 to prevent the gases from leaking out of the cell (sealing function). The sealing function is, however, spoiled when dimensional stability is lowered.
Further, because a large compressing force is applied to the cells in a state in which the cells are laminated, the separator 101 requires strength to withstand the compressing force. If the separator 101 is deformed, cracked or partially broken by the compressing force, the aforementioned gas-tightness or sealing property is spoiled undesirably. It is apparent also from this standpoint that increase in amount of the carbon type electrically conductive filler to be mixed is disadvantageous. That is, it is apparent that the strength of the separator 101 is lowered if the amount of the carbon type electrically conductive filler to be mixed is increased.
Furthermore, increase in amount of the electrically conductive filler to be mixed brings about a further problem that gas impermeability is lowered.
As described above, the techniques for obtaining the separator 101 for a fuel battery have problems as follows:
(1) In the method using glassy carbon, there is a problem in the cost of production.
(2) In the method using a resin material and an electrically conductive filler such as graphite powder, expansive graphite powder, or the like, there is a problem that it is difficult to make an electrically conductive property consistent with other requirements.
Therefore, the object of the present invention is to provide a technique of producing a separator for use in a fuel battery to satisfy simultaneously the following requirements:
the cost of production is low;
electrically conductive property is high;
gas-tightness is high;
dimensional stability is high (dimensional variation of products is small); and
mechanical strength is high.
In the present invention, attention is paid to the fact that a portion requiring great gas-tightness, great dimensional stability and great mechanical strength and a portion requiring a high electrically conductive property are distinguished from each other in a separator for a fuel battery obtained from a kneaded matter made of an electrically conductive filler and a resin material. Accordingly, the present invention is basically characterized in that optimum materials are used in the two portions respectively and a resin binder is contained in a collector portion.
In order to solve the above problems, there is provided a separator for a fuel battery having an electrically conductive property and being constituted by a collector portion provided with channels formed for making reactive gas flow through the channels, and a manifold portion having a composition different from that of the collector portion and provided with reactive gas introduction holes connected to the channels, the manifold portion being integrated with the collector portion so that a circumferential edge portion of the collector portion is surrounded by the manifold portion, wherein the collector portion contains a resin binder.
In order to solve the similar problems, there is provided a first method of producing a separator for a fuel battery comprising the steps of: forming the collector portion by using at least a resin binder and an electrically conductive filler as raw materials; and integrating the manifold portion with the collector portion by injection-molding a manifold portion-forming material of a composition different from that of the collector portion in the condition that the collector portion is disposed in a mold.
Further there is provided a second method of producing a separator for a fuel battery comprising the steps of: forming the collector portion by using at least a resin binder and an electrically conductive filler as raw materials; forming the manifold portion from a material different from that of the collector portion so that the manifold portion is divided into two in a direction of the plane of the manifold portion; and integrating the manifold portion with the collector portion in the condition that the collector portion is clamped by the manifold portion.
Further, there is provided a third method of producing a separator for a fuel battery comprising the steps of: forming the collector portion at least by using a resin binder and an electrically conductive filler as raw materials; forming a half of the manifold portion on one surface of the collector portion by injection-molding a manifold-portion-forming material of a composition different from that of the collector portion in the condition that the collector portion is disposed in a mold; and forming the other half of the manifold portion on the other surface of the collector portion by injection-molding the manifold-portion-forming material in the condition that the collector portion integrated with the one half of the manifold portion formed on the one surface of the collector portion is disposed in a mold.
The separator for use in a fuel battery according to the present invention is divided into a collector portion and a manifold portion. The collector portion is formed from a resin material which is mixed with a large amount of an electrically conductive filler so that the resin material has a high electrically conductive property at the sacrifice of gas-tightness, dimensional stability and mechanical strength.
On the other hand, the manifold portion is formed from a resin material which is mixed with a small amount of the electrically conductive filler or preferably contains no electrically conductive filler so that the resin material has gas-tightness, dimensional stability and mechanical strength preferentially. Further, because the manifold portion can be made to have high resistance (substantially, electrically insulating matter), there can be achieved a structure in which no current flows through the manifold portion so that there is no electric power loss caused by Joule heat. Further, generated electric power can be prevented from escaping from the manifold portion through a support portion. Further, containing of the resin material also in the collector portion satisfies the requirements of sealing function, dimensional stability, strength and moldability in the collector portion.
In this manner, a separator for a fuel battery with low electric power loss, high gas-tightness, high dimensional stability and high mechanical strength can be obtained.